Current vehicles are strongly required to reduce fuel consumption from the viewpoint of environmental protection. As a unit that reduces the fuel consumption, a downsized engine including a cylinder direct injection fuel supply device is being developed. The cylinder direct injection fuel supply device directly injects fuel in a combustion chamber by using a fuel injection valve (hereinafter called an injector) and can suppress abnormal combustion by cooling in the combustion camber. By suppressing the abnormal combustion, an engine can be downsized, and fuel consumption can be reduced. In the above-described downsized engine, a combustion chamber capacity is reduced, and a distance between the above-described injector and a wall surface is shortened. Therefore, injected fuel is easily attached on a piston crown surface and a wall surface of such as a cylinder. The attached fuel is introduced in a crank case by being scraped off by a piston ring and dissolved in engine oil. As a result, the engine oil is diluted by the fuel (hereinafter called oil dilution), and lubrication performance is deteriorated.
Therefore, for example, PTL 1 discloses a heating device for a lubricant in an internal combustion engine. In the heating device, an oil pump is provided which defines a lubricant heating chamber in a crank case of the internal combustion engine and force-feeds, in the heating chamber, the lubricant in a lubricant reservoir provided at a lower portion of the crank case, an outlet which causes the lubricant stored in the chamber to overflow and circulate in the lubricant reservoir is opened on a partition wall of the lubricant heating chamber, a breather port communicated with a gap provided at an upper portion in the chamber is opened in the lubricant heating chamber, the breather port is communicated with a breather chamber formed at an upper portion of the crank case, and the heater which operates when an oil temperature in the lubricant reservoir is at a predetermined temperature or lower and heats the lubricant stored in the chamber is provided in the lubricant heating chamber.
In addition, for example, PTL 2 discloses an engine oil dilution prevention device. The engine oil dilution prevention device includes a detection unit, a heating device, and a control unit. The detection unit detects a parameter on a dilution ratio of engine oil. The heating device heats the engine oil. The control unit causes the heating device to operate based on a result of a comparison between the parameter detected by the detection unit and a predetermined threshold.
In addition, for example, PTL 3 discloses a diluted oil regeneration device. The diluted oil regeneration device includes an injector, a regeneration timing detection unit, an oil heating unit. The injector supplies fuel to an engine. The regeneration timing detection unit detects a timing to regenerate engine oil diluted by the fuel injected from the injector. The oil heating unit heats and regenerates the engine oil diluted by the fuel at the timing to regenerate engine oil, and the oil heating unit heats engine cooling water.
In addition, for example, PTL 4 discloses an oil dilution suppression device. The oil dilution suppression device is mounted in a vehicle including an engine in which alcohol fuel can be used. The oil dilution suppression device includes an intake air amount integrating unit, a temperature detection unit, and a control unit. The intake air amount integrating unit calculates an integrated intake air amount by integrating the amount of air taken in the engine while the engine is operated. The temperature detection unit detects a temperature of engine oil of the engine. The control unit controls the vehicle so as to shift to an oil heating mode in which the oil temperature is increased in the case where the calculated integrated intake air amount is larger than an integrated intake air amount threshold and in the case where the detected oil temperature is lower than a first temperature threshold. PTL 4 discloses that a target heating temperature in the oil heating mode is set in consideration of a boiling point of alcohol fuel.